Co-pending patent application having Ser. No. 11/326,873, filed Jan. 6, 2006, discloses a system comprising a structure, a vortex induced vibration monitoring system, adapted to monitor a vortex induced vibration level of the structure, a tensioner connected to the structure, and a controller adapted to calculate a tension on the structure to optimize the vortex induced vibration value of the structure. Patent application Ser. No. 11/326,873 is herein incorporated by reference in its entirety.
Co-pending patent application having Ser. No. 10/228,385, discloses apparatuses and methods of monitoring fatigue, structural response, and operational limits in structural components. More particularly, the application relates to fatigue, response, and operational monitoring systems on steel catenary risers using optical fiber sensors. The sensors can be pre-installed on new risers, or post-installed sub-sea on existing risers, using a variety of methods. Patent application Ser. No. 10/228,385 is herein incorporated by reference in its entirety.
Referring to FIG. 1, there is illustrated prior art system 100. X axis 102, Y axis 104, and Z axis 106 are all defined. System 100 includes vessel 110 floating in water 112. Structure 114 is connected to vessel 110, and structure 114 goes to bottom 116 of water 112. Current 118a, 118b, and 118c are all traveling in the X direction, and encounter structure 114. Vortexes 120a, 120b, and 120c are caused by the interaction of currents 118a-118c with catenary structure 114. Vortex induced vibrations (VIV) 122a, 122b, and 122c are caused by interaction of currents 118a-118c with catenary structure 114. Vortex induced vibrations (VIV) 122a, 122b, and 122c may cause dynamic tensions of various values along the length of structure 114. In addition, vessel 110 may heave up and down due to wave actions, which may also cause dynamic tensions of various values along the length of structure 114.
Dynamic tensions along the length of structure 114 may be a concern because if the dynamic tension exceeds a critical value the structure may break, and/or lower values of dynamic tension over time may lead to a fatigue failure of the structure. It is desired to monitor the dynamic tension values along the length of structure 114 over time.
As illustrated in FIG. 1, a plurality of sensors 150 may be placed along the length of structure 114 to measure the dynamic tension of structure 114 where the sensor 150 is placed. It may be difficult to install and/or maintain multiple sensors 150 at multiple locations along the length of structure 114.
There is a need in the art for systems and/or methods to monitor stress and/or tension in structures exposed to a current or wind or heave. There is a need in the art for improved systems and/or methods to monitor dynamic tension values in structures exposed to a current or wind or heave with a reduced number of sensors.